1. Field of the Invention
The present invention relates to an electric vehicle that includes a wheel-driving motor. The electric vehicle of the present invention also includes: a hybrid vehicle that includes a vehicle-driving motor; and an engine and a fuel-cell vehicle.
2. Description of Related Art
In contrast to engine-driven vehicles, electric vehicles include an electrical system that utilizes high currents and that includes a wheel-driving motor, a high-capacity/high-output-current battery, an inverter that converts DC power of the battery into AC power suitable for driving the motor, and so on. Thus, there are various safety measures and preventive procedures for the electrical system, which are different from those for engine-driven vehicles.
For example, the inverter includes a large-capacitance capacitor that smoothes a high current that is input from the battery or a high current that is output to the motor. Japanese Patent Application Publication No. 2003-199387 (JP 2003-199387 A) proposes a technique to discharge electric charge of a large-capacitance capacitor in an inverter when a main switch of a vehicle (a so-called ignition switch) is switched OFF. According to the technique disclosed in JP 2003-199387 A, when the main switch is switched OFF, a switching device of the inverter is appropriately driven with a battery disconnected from the inverter to discharge electric charge of the capacitor.
The inverter generates heat because it to utilize high currents. The motor also generates heat. Therefore, many of electric vehicles include a cooling system that cools the inverter and the motor. The cooling system typically uses a liquid cooling medium, and includes a pump that delivers the cooling medium to the inverter and the motor. When the main switch of the vehicle is switched OFF or when a drive system of the vehicle is suddenly stopped due to any accident (a collision, for example), a supply of electric power to the pump is also stopped. However, the pump itself continues rotating due to an inertial force of the cooling medium that has been flowing. This causes a motor of the pump (hereinafter sometimes referred to as “pump motor”) to generate a counter electromotive force. If a current caused by the counter electromotive force is not dissipated anywhere, the motor of the pump can possibly be damaged. Particularly, in a case where the vehicle collides with an obstacle, if the drive system of the vehicle is suddenly stopped and the cooling system for the inverter and/or the motor is suddenly stopped, the pump motor can possibly be damaged by the counter electromotive force generated by the pump motor. Preventing the pump motor from being damage is also one of the measures specific to electric vehicles. The present invention disclosed herein has been made to solve the above problems.